The present invention relates generally to a system and method for engine braking in internal combustion engines. In particular, the present invention relates to an engine braking system and method for producing main, compression-release, bleeder, exhaust gas recirculation, and/or other auxiliary engine valve events combined with exhaust pressure regulation and turbocharger control.
Flow control of exhaust gas through an internal combustion engine has been used in order to provide vehicle engine braking. Generally, engine braking systems may control the flow of exhaust gas to incorporate the principles of compression-release type braking, exhaust gas recirculation, exhaust pressure regulation, and/or bleeder type braking.
The operation of a compression-release type engine brake, or retarder, is well known. During engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. During engine braking operation, as the piston approaches the top dead center (TDC), at least one exhaust valve is opened to release the compressed gases in the cylinder to the exhaust manifold, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine develops retarding power to help slow the vehicle down. An example of a prior art compression release engine brake is provided by the disclosure of the Cummins, U.S. Pat. No. 3,220,392 (November 1965), which is hereby incorporated by reference.
The principles of exhaust gas recirculation (EGR) are also well known. An EGR system allows a portion of the exhaust gases to flow back into the engine cylinder and is primarily used to reduce the amount of NOx created by the engine during positive power operations. An EGR system can also be used to control the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate exhaust gases back into the engine cylinder through an intake valve(s). Internal EGR systems recirculate exhaust gases back into the engine cylinder through an exhaust valve(s).
Furthermore, control of EGR may be achieved by selectively varying the levels of exhaust back pressure using Exhaust Pressure Regulation (EPR). By controlling EGR with EPR, the levels of pressure and temperature in the exhaust manifold and engine cylinders may be maintained such that optimal degrees of engine braking are attained at any engine speed. An example of a method and system for optimizing engine braking using EGR and EPR is provided by the disclosure of Israel, U.S. Pat. No. 6,170,474 (Jan. 9, 2001) for Method and System For Controlled Exhaust Gas Recirculation in an Internal Combustion Engine With Application to Retarding and Powering Function, which is hereby incorporated by reference.
The operation of a bleeder type engine brake has also long been known. During engine braking, in addition to the normal exhaust valve lift, the exhaust valve(s) may be held slightly open continuously throughout the remaining engine cycle (full-cycle bleeder brake) or during a portion of the cycle (partial-cycle bleeder brake). The primary difference between a partial-cycle bleeder brake and a full-cycle bleeder brake is that the former does not have exhaust valve lift during most of the intake stroke.
Usually, the initial opening of the braking valve(s) in a bleeder braking operation is far in advance of the compression TDC (i.e., early valve actuation) and then lift is held constant for a period of time. As such, a bleeder type engine brake requires much lower force to actuate the valve(s) due to early valve actuation, and generates less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake. Moreover, bleeder brakes often require fewer components and can be manufactured at lower cost. Thus, an engine bleeder brake can have significant advantages.
Despite these advantages, however, bleeder type engine brakes have not been widely used because they typically produce less braking power than the compression-release type brakes in heavy duty diesel engines with a conventional fixed geometry turbocharger (FGT). This reduced braking power occurs especially at low and moderate engine speeds.
With the introduction of variable geometry turbochargers (VGT), however, bleeder brakes become a more attractive option. Through the use of VGT, both the intake and exhaust manifold pressures may be much higher than those produced using conventional FGT. These increased pressures may correspond to greatly improved bleeder brake performance, especially at low and moderate engine speeds.
The prior art methods and systems do not disclose incorporating VGT to improve bleeder braking performance. For example, Falefti et al., U.S. Pat. No. 6,148,793 (Nov. 21, 2000), discloses a compression-release type braking system utilizing a variable geometry turbocharger, but does not disclose a bleeder braking system using VGT for optimizing engine braking. Similarly, Church et al., U.S. Pat. No. 6,134,890 (Oct. 24, 2000), discloses a method for controlling VGT for providing precise control of turbo boost pressure. The ""890 patent does not, however, disclose a system and method utilizing VGT to control exhaust back pressure for improving bleeder braking performance.
Also, Price et al., U.S. Pat. No. 4,395,884 (Aug. 2, 1983) and U.S. Pat. No. 4,474,006 (Oct. 2, 1984), disclose principles similar to those of a variable geometry turbo to control engine braking, but do not disclose methods and systems of engine bleeder braking using VGT. In addition, A. Flotho et al., xe2x80x9cNew Engine Brake Systems for Commercial Vehiclesxe2x80x9d (1999), which is hereby incorporated by reference, discloses a two-stage turbocharger adapted to enhance engine braking, but the geometry of the turbocharger is not variable. Accordingly, there is a significant need for a method and system for engine braking in an internal combustion engine with VGT that captures the inherent advantages of bleeder braking operation and provides improved bleeder braking performance.
Current variable geometry turbochargers typically include a mechanical stop that prevents the geometry (vanes) of the VGT from fully closing. This is so because, once the vanes are fully closed, the significant pressure gradient across the VGT creates control instability and prevents the vanes from being re-opened. The mechanical stop of most VGTs is based on optimum engine positive power operation, and is usually not optimum for engine braking. This means that the increased exhaust manifold pressures created below this position, and, thus, opportunities for improved engine braking, may be forfeited.
None of the prior art methods and systems teach or suggest minimizing the pressure gradient across the VGT to avoid control instability and maximize the VGT geometry variation range. Accordingly, there is an additional need for a method and system for controlling engine braking in an internal combustion engine with VGT that captures the advantages of bleeder braking operation but eliminates or reduces the limitations caused by the mechanical stop features of conventional variable geometry turbochargers. FIG. 1 illustrates an example of a comparison between improved bleeder brake performance results in a full-cycle bleeder braking system with VGT according to the present invention obtained by the present Assignee and performance using conventional VGTs with the mechanical stop limitation.
In addition, the braking performance of a bleeder braking system can be further optimized by using EGR and EPR to xe2x80x9ctunexe2x80x9d exhaust back pressure. By combining EGR and EPR with fully operational VGT, the levels of pressure and temperature in the exhaust manifold and engine cylinders may be maintained such that optimal degrees of engine braking are attained at any engine speed. None of the prior art systems and methods, of which the present inventors are aware, teach or suggest this combination.
The systems and methods of the present invention respond to the needs left unanswered by the prior art. The present invention provides systems and methods for improving bleeder brake performance using any combination of turbocharger control, EGR, and EPR. The present invention further provides systems and methods for eliminating or reducing the limitations caused by the mechanical stop features of conventional VGT so that the VGT variation range may be extended for wider application in both engine braking and positive power operations. In addition, the present invention provides improved mechanisms and devices to achieve a bleeder braking cycle.
It is, therefore, an object of the present invention to overcome the shortcomings present in known engine bleeder braking systems and methods.
It is an object of the present invention to improve performance of an engine braking system using turbocharger control.
It is another object of the present invention to improve performance of a bleeder brake system using VGT.
Another object of the present invention is to control the pressure gradient across a VGT turbine in order to avoid VGT control instability problems.
It is another object of the present invention to move the minimum hard stop in VGTs to a more closed position or eliminate the minimum hard stop altogether such that the VGT variation range may be extended for a wider application in both engine braking and positive power operations.
It is another object of the present invention to control the exhaust manifold pressure using a combination of VGT, pressure regulation valve(s), and/or a bleeder brake.
It is another object of the present invention to control the exhaust manifold temperature using a combination of VGT, pressure regulation valve(s), and/or a bleeder brake.
It is yet another object of the present invention to initialize a bleeder brake event with valve float (valve separating from its seat) controlled by EPR.
Another object of the present invention is to control EGR using EPR, VGT, and/or a bleeder brake.
Still another object of the present invention is to optimize bleeder braking performance at all engine speeds, especially at low and moderate engine speeds, without exceeding engine operating limits at high engine speeds.
It is another object of the present invention to provide an engine braking system that generates less noises than known engine braking systems.
Another object of the present invention is to provide an engine system that reduces the amount of NOx created by the engine.
Another object of the present invention is to provide a control method and system for engine bleeder braking using EGR, EPR, and VGT control.
Yet another object of the present invention is to provide various valve actuation subsystems for use in a bleeder brake engine braking system.
It is another object of the present invention to provide an engine braking assembly that uses high-pressure fluid to actuate at least one engine valve during an engine braking event.
Additional objects and advantages of the present invention are set forth, in part, in the description which follows, and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
The present invention is directed to a system and method for controlling the braking of an engine having intake and exhaust manifolds, at least one turbocharger, preferably, a variable geometry turbocharger, coupled between the intake and exhaust manifolds, and at least one intake and exhaust valve. The method of the present invention may include the steps of measuring an engine parameter to produce a measured value; regulating the pressure of the exhaust manifold based on the measured value; actuating the at least one exhaust valve; and controlling the pressure gradient across the variable geometry turbocharger.
In another embodiment, the present invention is a method for improving the performance of a bleeder braking operation for an engine having intake and exhaust manifolds and at least one intake and exhaust valve. The method of the present invention may include the steps of controlling the geometry of a turbocharger, preferably, a variable geometry turbocharger to provide optimal engine braking; regulating the exhaust manifold pressure to avoid engine limitations from being exceeded; actuating the at least one exhaust valve for a bleeder braking cycle; and controlling the pressure gradient across the variable geometry turbocharger to avoid control instability.
In another embodiment, the present invention is directed to a system for controlling the braking of an engine, during an engine braking event, having intake and exhaust manifolds and at least one intake and exhaust valve. The system may include a variable geometry turbocharger coupled between the intake and exhaust manifolds; pressure regulating means for regulating the pressure in the exhaust manifold and the pressure gradient across the variable geometry turbocharger; valve actuation means for actuating the at least one exhaust valve during an engine valve event; and control means for controlling the pressure regulating means and the valve actuation means during the engine valve event.
In yet another embodiment, the present invention is a method for improving braking performance of an engine having intake and exhaust manifolds, a turbocharger, preferably, a variable geometry turbocharger coupled between the intake and exhaust manifolds, at least one intake and exhaust valve, and at least one pressure regulation valve. The method uses an exhaust gas recirculation event and a bleeder braking valve event and may comprise the steps of generating exhaust gas back pressure in the engine; monitoring an engine parameter level to produce a measured parameter; carrying out the exhaust gas recirculation event responsive to the measured parameter; controlling the flow area and/or the direction of exhaust gases through the turbocharger responsive to the measured parameter; and regulating the pressure in the exhaust manifold responsive to the measured parameter.
In another embodiment, the present invention is an engine braking assembly for producing a braking event in an engine having at least one engine valve biased in the closed position by an engine valve spring, at least one engine cylinder, and intake and exhaust manifolds. The engine braking assembly may comprise a housing, having a hydraulic circuit formed therein; a high-pressure fluid source adapted to store high-pressure fluid therein; a supply valve assembly adapted to receive high-pressure fluid from the high-pressure fluid source; a control assembly for selectively controlling the supply of the high-pressure fluid from the high-pressure fluid source to the supply valve assembly and operating the supply valve assembly; and a valve actuation assembly, in communication with the supply valve assembly through the hydraulic circuit, wherein the valve actuation assembly receives the high-pressure fluid from the supply valve means and wherein the pressure created by the high-pressure fluid actuates the at least one engine valve.
In another embodiment, the present invention is an engine braking assembly for producing a braking event in an engine having at least one engine valve, at least one engine cylinder, and intake and exhaust manifolds. The engine braking assembly of the present invention may include a rocker arm having at least one hydraulic passageway for receiving hydraulic fluid, a first bore, and a second bore formed therein; a valve assembly located within the first bore of the rocker arm, the valve assembly selectively controlling the flow of the hydraulic fluid in the at least one hydraulic passageway to control the operation of the braking event; and a piston assembly located within the second bore of the rocker arm, the piston assembly in communication with the valve assembly through the at least one hydraulic passageway and adapted to receive the hydraulic fluid. The pressure created by the hydraulic fluid and/or by a pressure differential across the at least one engine valve created by pressure regulation means causes the piston assembly to actuate the at least one engine valve.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only. And are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference and which constitute a part of the specification, illustrate certain embodiments of the invention and, together with the detailed description, serve to explain the principles of the present invention.